This invention relates to the production of waferlike materials that require flat surfaces such as semiconductors. More particularly it involves an improvement in the method of slicing ingots or boules by providing an improved mounting beam for said ingots or boules.
The preparation of semiconductor substrates, such as silicon or gallium arsenide, for the fabrication of semiconductor devices requires a number of precisely controlled chemical and mechanical steps. The substrate material is first prepared in a very pure state by whatever preparation and refining methods are required. This material is then crystallized to provide a very large single crystal in the form of an ingot. These ingots are turned on a lathe to roundness, flattened on one side and then sawed or sliced into wafers that are lapped and polished to provide a flat surface for the production of sophisticated electronic components.
Slicing the ingots into wafers is a very important step in the process, since the wafers must be of uniform thickness, have a flat profile and be free of stress produced by slicing. One of the factors that is required to achieve these requirements is that the ingot must be held very securely during the slicing operation. The method currently used involves bonding the ingot to a cutting or mounting beam, usually graphite, with an epoxy adhesive. The graphite cutting beam is coated with the adhesive, and the silicon ingot is placed on the beam. The epoxy is then allowed to cure before a diamond saw is used to slice the ingot into wafers. The wafers are removed from the cutting beam by mechanically and/or chemically breaking the epoxy adhesive bond.
The inside diameter saw is impregnated with diamond and/or other abrasives. In addition to sawing the semi-conductor ingot and epoxy adhesive, the saw penetrates the mounting beam as well. In contacting these various materials the saw blade acquires various deposits which if allowed to accumulate affect blade life, product quality, kerf loss and slicing speed. At present these adverse effects are ameliorated by use of a dressing stick applied to the saw blade by a human operator.
Automated mechanical dressing tools have been suggested, but have not found acceptance. A. D. Morrissey of The Jet Propulsion Laboratory has suggested that patches of blade dressing material be inserted into the mounting beam. See NASA Tech Brief Vol. 8, No. 31 Item #134.